Species composition of the biospere



  • Intricate webs of interacting organisms
    • ~2,000,000 species are described
    • ~18,000 plants & animals discovered yearly
    • estimated >85% of species unknown


  • Current composition reflects billions of ways organisms have adapted, over and over, to a changing planet


  • Humans have altered 75% of ice-free surface
    • alters species composition
    • alters livable habitats
    • alters climate

“Essay of the geography of plants” by Humboldt, 1817


Underlying causes of the uneven distribution of plants….


Humboldt’s lessons: Species are spatially arranged


Humboldt lessons: Species are spatially arranged


Similar biological communities reside within our biomes


Climate drives broad distribution of terrestrial biomes


Biomes also have distinct soil types


Species distribution varies widely within biomes


Seasons may impact species distributions


Migration can cross many biomes: Birds


Species may instead be adapted for seasonal habitats


Niche defines the limiting tolerance factors for a species


Ecological Niche =

Tolerance Ranges: Coral Reefs


Ecological niches exist in n-dimensions (many factors)


Distribution of species within biological communities overlap


Fundamental vs Realized Niche =

Species distributions are related to their realized niche space

Species distributions are related to their realized niche space

Species ranges versus distribution: Crocodiles


Species ranges versus distribution: Crocodiles


Ranges versus distribution: Plants more limited by dispersal


dispersal: movement of individuals or gametes
seed dispersal: gravity, wind, water, and by animals

Species ranges versus distribution: Coconut tree


Biogeography and animal ranges: Alfred Wallace 1859


Wallace developed theories of evolution at the same time as Darwin to explain the patterns in biogeography he observed

Zoogeographic regions: Wallace